The trifluoroacetylation of basic amino acids, such as lysine or ornithine, among others, using trifluoroacetic anhydride in an acid medium is known (Weygand et al., Chem. Ber. 89, 647 (1956)). It has been observed in such prior art processes that the trifluoroacetylation reaction of amino acids containing two amine groups preferentially takes place on the amine group in the .alpha.-position relative to the carboxyl group, or simultaneously on the two amine groups.
The trifluoroacetylation of the amine group at the end of the chain of amino acids such as lysine and ornithine, by reacting such acids with ethyl thioltrifluoroacetate in an aqueous basic medium, has been proposed (Schallenberg et al., Journal of American Chem. Soc. 77,2779, (1955)). Ethyl thioltrifluoroacetate, however, is a material which is expensive, polluting, and unavoidably gives an odor of sulfur to the amino acid prepared. Additionally, although Schallenberg et al. indicates that N-.omega.-trifluoroacetylation occurs, it has been found that this process does not enable saturated aliphatic monocarboxylic .alpha.,.omega.-diamino acids to be N-trifluoroacetylated in the .omega.-position with an adequate selectivity. Indeed, it has been found that the process of Schallenberg et al. does not prevent .alpha.-trifluoroacetylated and .alpha.,.omega.-ditrifluoroacetylated derivatives from being formed in significant amounts.
T. J. Curphey (J. Org. Chem., 44 (15) 2805 (1979)) has described the N-trifluoroacetylation of .alpha.-amino acids containing a single --NH.sub.2 amine group, using ethyl trifluoroacetate in the presence of a triethylamine-type base and anhydrous methanol, over a period of at least fourteen hours The products obtained are N-.alpha.-trifluoroacetylated. The instant inventors have observed that saturated aliphatic monocarboxylic .alpha.,.omega.-diamino acids are not N-trifluoroacetylated regioselectively at the .omega.-position when treated by the Curphey process.